Recently, as the digital technology has advanced and has become more popular, it has become possible to digitally record or play back a variety of music data, image data, etc. to or from a recording medium. As a result, it has become possible to obtain data not lower in image or sound quality than its original data even after repeating data copying a plurality of times.
With the development of the digital technology, however, the following problems have occurred:
(1) For example, when a digital music data is copied from a compact disc (CD) to a hard disc of a personal computer, the music data from the CD can be recorded as it is or compressed into the hard disc, so that the music data will be distributed fraudulently in a large volume via a network such as the Internet.
(2) When a digital music data is copied from a CD to a hard disc of a personal computer, the music data will be distributed in a large volume since the number of copies is not limited.
(3) When a digital music data is copied from a hard disc of a personal computer to an external apparatus such as portable device, the original digital music data will remain in the hard disc after the copying, so that it will possibly be copied and distributed in a large volume.
(4) To prevent the problem (3) above, the software for the personal computer should be designed so that after the digital music data is copied to the external apparatus, the data in the hard disc being the data source is erased (the music data is moved). However, if the content in the hard disc is backed up in another recording medium before it is moved and the data thus backed up is restored to the hard disc after the move, the data having been moved will remain in the hard disc.
(5) When a digital music data in a hard disc of a personal computer is copied to an external apparatus such as portable device, it will possibly be passed to an illegal apparatus since it is not confirmed of what type the external apparatus is.
When a digital music data is passed from an external apparatus such as portable device to a personal computer, it will possibly be passed to an illegal software since it is not confirmed of what type the software controlling the personal computer is.
(6) When a music data reproduced from a CD is dealt with in a personal computer, ISRC (International Standard Recording Code) included in the music data can be used to judge whether one music piece is the same as the other. However, no ISRC data is included in the CD as the case may be. In this case, it is not possible to judge whether the music pieces are the same as each other.
(7) The above functions can be performed under the control of a software in a personal computer. So, if the software itself is altered, an operation not intended by the system designer will possibly be done.